Capacitive high-frequency heating apparatus

ABSTRACT

An apparatus for uniform capacitive heating of bands of dielectric material such as paper and the like has two electrode groups arranged in respective mutually parallel planes. Each of the electrode groups includes a plurality of rod-like electrodes equally spaced in a row and each of the electrodes of one of the groups lies opposite a corresponding one of the electrodes of the other group. A feed system is arranged in a third plane intermediate the two electrode groups and includes a plurality of individual rods, each of said rods being disposed between a corresponding pair of said opposite electrodes. A high-frequency supply is provided for supplying the feed systems and the rods are alternately connected with different poles of the supply. A contactor is slidably mounted between each of the rods and the corresponding pair of opposite electrodes.

United States Patent Grassman Y [72] Inventor: Hans Christian Grassman, lgelsdorfi.

Germany [73] Assignee: Siemens Aktiengesellschaft, Munich,

Germany 22 Filed: June 2,1971

[211 App]. No.: 149,261

[30] Q Foreign Application Priority Data June 5, 1970 Germany ..P 20 27 674.8

[52} US. Cl. 219/1061, 34/1 [5i] Int. Cl ..H05b 5/00 [58] Field of Search ..219/10.6l, 10.55; 34/1 [56] References Cited UNITED STATES PATENTS 3,469,054 9/1969 Serota ..2l9/l0.6l 3,119,920 l/l964 Mayhew ..34/1 X 1 Aug. 1, 1972 PrimaryExaminer-J. V. Truhe Assistant Examiner-Gale R. Peterson Attorney-Curt M.- Avery, Arthur E. Wilfond, Herbert L. Lerner and Daniel J. Tick 1 [57 ABSTRACT opposite electrodes. A high-frequency supply is provided for supplying the feed systems and the rods are alternately connected with different poles of thesupply. A contactor is slidably mounted between each of the rods and the corresponding pair of opposite electrodes.

3 Claims, 4 Drawing Figures PATENTEDAUQ 1 I972 SHEET 2 BF 2 wv i Fig. 4

CAPACITIVE HIGH-FREQUENCY HEATING APPARATUS My invention relates to an apparatus for uniform capacitive heating of wide bands of dielectric material, especially paper, wherein the bands are movable past a stray field of electrode groupings. These electrode groupings each comprise a plurality of rod-like individual electrodes, disposed next to each other in row and equally spaced. The electrodes are alternately fed with high-frequency voltage of alternating or different polarities.

Dielectric heating apparatus can be equipped with stray field electrodes wherein the electrode rods form a row of capacitors with air dielectric. If a material that is to be heated is brought to the vicinity of the electrodes for example, to a distance of approximately to percent of the distance betweenneigh-boring rods, then the field between the rods is so deflected that it goes through the material. The intensity of the field deflection is dependent upon the dielectric loss factor (cthu tan 8) of the material.

Stray field electrodes are used with success in continuous production methods especially for handling thin layers of material, for example, to dry leather, paper, carpets, etc.

By heating bands of this type difficulties arise if the width of the electrode arrangement lies in the region of the wave-length used. Since standing waves occur, there arises voltage maximums and voltage minimums along the capacitorfield electrodes. Even when the length of the electrode rods does not exceed one-fourth of the wave-length, there occurs an increase in voltage when high frequency voltage is applied, the voltage increase being viewed from the feed point of the treating electrodes to the corresponding end of the treating electrodes. This voltageincrease becomes ever more evident the closer the length of the electrode rods come to a M4 wave-length.

In the art, it has been determined that with electrode systems which are longer than one-twentieth of the wave-length, voltage excesses occur which lead to a non-uniform heating of the material or goods to be heated.

It is known to prevent excessive voltage changes along the electrodes to connect coils to the ends of the treating electrodes which are so dimensioned that the voltage maximum is displaced to the mid-region between the electrodes. It is also known in the art to divide the field electrodes in component parts and to supply the latter via taps of special high frequency lines. In this connection reference may be had to German Pat. No. 886,193. All these measures, however, provide only limited assistance and the related equipment is especially expensive to construct. I

Accordingly, it is an object of my invention to provide an apparatus of the above-mentioned type having electrodes of a length of up to one-fifth of the wavelength of the applied frequency wherein a voltage distribution is provided which is uniform to within several percent.

To this end and according to the invention I provide an apparatus of the above-mentioned type having two electrode groups lying in respective mutually opposite parallel planes. A feed system is provided whose individual rods are disposed in a third plane between the two parallel planes. The individual rods are connected alternately with different poles of the high frequency source. Each of the electrodes of one of the groups lies 7 opposite a corresponding one of the electrodes of the other group. Each of the rods is between a corresponding pair of the opposite electrodes and connected with the latter via contact slides movable in the rod direction. By displacing the contact slider and in combination with the central feed tube, a voltage distribution in the longitudinal direction of the stray field electrodes is influenced and made uniform.

Through this arrangement of the electrodes there is obtained a space saving heating system that functions economically since the electrode system can be built with small capacitance values and therefore with small self loss.

In an especially advantageous embodiment of the invention each individual rod is connected with its both ends to the same pole of the high-frequency source and, with electrode arrangement of M5, two contact sliders are arranged M15 from each end respectively. In this way, a voltage constant to within plus or minus 1.5 percent is obtained. Without the central feed a voltage change in the direction along the electrodes of up to 20 percent would occur.

In addition tothe measures already described, the electrodes can be subdivided into sets or groups in the longitudinal direction for obtaining a more uniform distribution of the field. Also for obtaining a more even field distribution, the generators can be compensated by means of suitable chokes and/or capacitors as well as by other known techniques applied.

The invention will now be described with reference to the drawing wherein:

FIG; 1 is a plan view of a capacitive high-frequency heating apparatus according to the invention;

FIG. 2 is a view of the apparatus of FIG. 1 taken along the line II-II;

FIG. 3 illustrates the voltage distribution on a rodlike electrode; and,

FIG. 4 illustrates how the electrodes can be arranged in groups or sets which are supplied separately to obtain a more uniform field distribution.

Referring to FIG. 1, a band of paper 1 to be dried having a width of 4 meters is guided in the direction of arrow 2 first through the stray field e of the stray field electrode grouping 11. Next, the paper band 1 is directed over a directional roller 3, and then, through the stray field of the stray field electrode grouping 13. The stray field electrode grouping 11 and 13 are comprised of respective pluralities of rod like electrodes 5 and 7. The electrodes of each grouping are arranged in a plane and spaced at equal distances from each other. The electrodes 5 and 7 are alternately supplied with a high frequency voltage of different polarities.

A voltage supply serves a feed system 12. The feed system or group 12 is arranged between the two stray field electrode groups 11 and 13 such that the three groups 11 to 13 lie in three mutually parallel planes. Each of the individual rods 6 of the supply system 12 is connected with corresponding ones of the electrodes 5 and 7 via contact sliders 9. The individual rods are connected at both ends at terminals 8 alternately with respective poles of the high-frequency source. The contact slider 9 is movable in the direction of the double arrow 10 and can, in combination with the individual treating frequency of f 13.56 MHz the length l of the electrodes 5 and 7 and of the individual rods 6 is approximately 4 meters and the width of the band 1 is likewise 4 meters.

This length corresponds to approximately one-fifth of the wave length. Both contact sliders 9 are approximately 13 meters (M15) distant from the ends of the individual rods 6. The spacing between the two contact sliders 9 amounts to approximately 1.4 meters.

FIG. 3 illustrates the voltage distribution on an electrode Ssupplied via contact slider 9. The broken line curve b shows the voltage U which results from the supply over a central feed system and curve a designates the voltage U, which would occur if the middle supply system were not available.

Preferably, the individual electrode groups, seen in the running direction of the running path, have a length corresponding to only approximately half the path width in order to guarantee a path transport without difficulties. With higher speeds, the required drying time can be obtained 'by means of several electrode systems connected one behind the other. FIG. 4 illustrates how the electrodes may be subdivided into sets and supplied separately from the highfrequency source. This arrangement functions to make the field of the electrodes uniform.

While the invention has been described by means of a specific example and in a specific embodiment, I do not wish to be limited thereto for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. Apparatus for uniform capacitive heating of bands of dielectric material such as paper and the like, comprising two electrode groups arranged in respective mutually parallel planes, each of said electrode groups including a plurality of rod-like electrodes spaced in a row equally, each of the electrodes of one of said groups lying opposite a corresponding one of the electrodes of the other group, a feed system arranged in a third plane intermediate said two electrode groups, said feed system including a plurality of individual rods, each of said rods being disposed between a corresponding pair of said opposite electrodes, high-frequency supply means for supplying said feed system, said rods being alternately connected with different poles of said supply means, and contact means slidably mounted between each of said rods and said corresponding pair of opposite electrodes.

2. Apparatus according to claim 1, each of said rods being connected at both its ends-to a like pole of said high-frequency supply means, said electrodes having a length of one-fifth of the wavelength (A) of the operating frequency of said supply means, said control means comprising a plurality of sliding contacts, each two of said co tacts bei arran ed 'th r s ct to a correspon ing one o s aid roo for electri c lly connecting the latter and said corresponding pair of said opposite electrodes, said two contacts being positioned a distance of M15 from said ends of said corresponding one of said rods respectively.

3. Apparatus according to claim 1, said electrode pairs being grouped into sets in the direction of said rows, said sets being supplied from said supply means separately from each other. 

1. Apparatus for uniform capacitive heating of bands of dielectric material such as paper and the like, comprising two electrode groups arranged in respective mutually parallel planes, each of said electrode groups including a plurality of rod-like electrodes spaced in a row equally, each of the electrodes of one of said groups lying opposite a corresponding one of the electrodes of the other group, a feed system arranged in a third plane intermediate said two electrode groups, said feed system including a plurality of individual rods, each of said rods being disposed between a corresponding pair of said opposite electrodes, high-frequency supply means for supplying said feed system, said rods being alternately connected with different poles of said supply means, and contact means slidably mounted between each of said rods and said corresponding pair of opposite electrodes.
 2. Apparatus according to claim 1, each of said rods being connected at both its ends to a like pole of said high-frequency supply means, said electrodes having a length of one-fifth of the wavelength ( lambda ) of the operating frequency of said supply means, said control means comprising a plurality of sliding contacts, each two of said contacts being arranged with respect to a corresponding one of said rods for electrically connecting the latter and said corresponding pair of said opposite electrodes, said two contacts being positioned a distance of lambda /15 from said ends of said corresponding one of said rods respectively.
 3. Apparatus according to claim 1, said electrode pairs being grouped into sets in the direction of said rows, said sets being supplied from said supply means separately from each other. 